Effect of Initial Knee angle and Arm Facilitation on biomechanics of the Sit-to-Stand movement

Spinal cord injuries cause loss of muscle function and subsequently reduce independence. Therapeutic interventions such as transcutaneous spinal cord stimulation are increasingly being used to help improve motor functioning however, a comprehensive understanding of the biomechanical elements of movement may help optimize stimulation protocols. Twenty healthy participants completed five sit-to-stand (STS) transitions while initial knee angle and arm facilitation were altered. Electromyography (EMG) activation of four lower limb muscles and centre of pressure dynamics were recorded. Acute initial knee angles resulted in a change in duration of phases within the STS, and restrictive arm positioning caused the time to completion to increase (p=0.04). Muscle activation patterns across phases were compared and showed significant differences between phases in both the Tibialis Anterior and Rectus Femoris (p<0.006). Acute initial knee angles were also found to significantly increase Biceps Femoris activation across multiple phases (p=0.034). Altering the starting position and limb movement result in vastly different temporal and muscular strategies to complete the STS. Thus, joint angle and upper limb facilitation should be considered when designing rehabilitative interventions for clinical cohorts.